Photoelectric tube



F. M. PENNING PHOT OELECTRIC TUBE Filed March 15, 1935 INVENTOR. FRANZ M. PENNING TTONEY.

Patented Feb. 18, 1936 UNITED STATES PHOTOELECTRIC TUBE Frans Michel Penning, Eindhoven, Netherlands, assignor to Radio Corporation of America, a corporation of Delaware Application March 13, 1935, Serial No. 10,768 In Germany March 14, 1934 4 Claims.

My invention relates to light sensitive devices and in particular to improvements in photo-electric tubes.

It has been proposed to amplify the current 5 dislodged from the photo-electrically active cathode of a photo-electric tube by equipping the latter with a cathode and an anode and in addition with a third electrode which is of such a nature and has such a tension with respect to the other 10 electrodes, that the primary photo-electric current strikes it and dislodges secondary electrons therefrom. The quantity of electrons dislodged from the third electrode is found to be greater than that of the impinging electrons received 15 from the first or primary cathode electrode. Preferably, the auxiliary electrode consists of alkali-metal at its surface, and is given a positive voltage with respect to the cathode. However,

this voltage is given a smaller value than the anode voltage.

Consequently, two different voltages, viz. the anode cathode voltage and the auxiliary electrodecathode voltage must be supplied to the electrode of the tube. Therefore, the latter must be pro- 25 vided at least with three supply members, for instance, with a base having three contact pins.

The invention which relates to a photo-electric tube comprising an anode, a cathode and in addition an auxiliary electrode adapted for the emis- 0 sion of secondary electrons, has for its purpose to avoid the use of two different voltages.

According to the invention the auxiliary electrode is connected for this purpose to the photoelectric electrode through a high resistance which,

35 for example, may .be of the order of magnitude of to 100 megohms. It has been found that in this tube amplification of the primary photoelectric current by secondary emission is achieved, without a special voltage being supplied 40 to the auxiliary electrode. Preferably the resistance is incorporated in the tube and arranged, for instance, within the tube or within the base so that the number of outer contacts may be the same as in the absence of the auxiliary electrode. 45 Thus the tube according to the invention may replace a similar tube not including an auxiliary electrode, without modifying the apparatus in which the tube is used.

The invention will be more clearly understood by reference to the accompanying drawing in which Figure 1 represents, by way of example, a photo-electric tube embodying my invention; Figure 2 is a graph showing the relation of ourrent and light intensity; and Figure 3 is a modified form of invention showing the resistor within the envelope.

The highly exhausted bulb-shaped vessel or en- Velope of the tube is denoted by I, two electrodes 2 and 3 being provided on the inner side of the 5 wall of the tube. The first-mentioned electrode constitutes a light responsive or photo-electrically active cathode which is irradiatedthrough the window 4 provided in the electrode 3, the latter being separated from and therefore insulated from the cathode 2 and constituting the auxiliary electrode where the secondary emission occurs. Both electrodes may be manufactured in the same manner and each consists, for instance, of a silver mirror which is deposited on the wall of the bulb, superficially oxidized, and subsequently exposed to the action of alkali-metal, for instance, caesium. Further, the tube comprises an anode 5 which is shaped as a grid and consists, for instance, of wire mesh or gauze. Anode 5 forms in effect a partition dividing the space of the tube in two parts. In the case of a transparent auxiliary electrode thewindow 4 in the auxiliary electrode may be dispensed with. The invention also applies to tubes having a gasfilling.

The electrodes are connected to supply wires which are led out through the press 6. The wire I connected to the auxiliary electrode 3 is secured to one end of the resistance 9 which is provided in the reentrant stem 8 and whose other end is connected to the supply or lead-in wire In of the photo-electrically active cathode 2. The tube is equipped with a base I I having two contact pins l2 and I3. These contacts are connected to the wire Ill and to the wire M respectively, the latter supplying anode current. It will be seen that the resistance 9 may, if desired, also be provided within the tube or in or at the base, or again be arranged so as to be separated from the tube.

Figure 2 indicates the space current strength as plotted against the flux of light falling on the photo-electric cathode 2. This curve was measured for a cathode-anode voltage of 500 volts and a resistance of 53 megohms between the auxiliary electrode and the cathode.

As appears from Figure 2, the curve has not exactly the same course with an increasing as with a decreasing flux of light. I he size of the loop formed by the curve depends on the value of the resistance 9. In certaincases this loop will cause trouble so the light flux should be adjusted.- to the curve part beyond the loop. In other cases when, for instance, the tube is used 55 contact pins, a light responsive cathode in said tube, a second cathode positioned to receive electrons from the first mentioned cathode, an anode and a resistor in said tube connected at one end to said second cathode and at the other end to the first mentioned cathode and one of said contact pins.

3. A photo-electric tube comprising an envelope supported on a base, and contact pins, a cathode comprising a coating of light responsive material on one wall of said envelope, a second cathode on the opposite wall of said envelope with an opening to admit light to the first mentioned cathode, an anode between said cathodes, and a resistance connected between said cathodes.

4. A light responsive device comprising an envelope with a'press, lead-in wires in said press a photo-electrically active cathode in said envelope, an auxiliary cathode electrode in said envelope insulated from the first mentioned cathode, a window in the wall of said envelope to admit light to the interior thereof, an anode electrode in said envelope connected to one leadin wire, a second lead-in wire connected to said photo-electrically active cathode, and a resistor connecting said second lead-in wire to said auxiliary cathode electrode.

FRANS MICHEL PENNING. 

